Diamond powders are widely used in abrasive applications in which diamond particles of a wide range of diameters are either bonded on a variety of tools for drilling, sawing, grinding, cutting, slicing, etc., or bonded to form diamond films or incorporated into slurries and compounds for lapping and polishing applications. In addition, diamond particles can be sintered under high pressure-high temperature (HP-HT) conditions to form an abrasive body/compact (polycrystalline diamond compact or PCD).
The production of high performance diamond tools requires that diamond particles be firmly retained in the bonding material in which they are embedded. A variety of bonding materials are used for the manufacturing of diamond tools, including: metals and metal alloys, glass, ceramics and synthetic resins. The bonding between diamond particles and the bonding material can be mechanical or chemical. Mechanical bonding is when bonding material envelops the diamond particles. In contrast, chemical bonding is when diamond particles react with bonding material to form chemical bonds at the diamond-bonding material interface. Conventional regular monocrystalline diamond particles exhibit smooth surfaces at which bonding occurs. However, bonding strength improves if diamond particles exhibit a rough surface having increased surface area available for bonding, resulting in increased bond retention.
Lapping and polishing of advanced materials wafers (i.e. sapphire, silicon carbide, gallium nitride, gallium arsenide, etc) used in electronics industry require substantially scratch free, high surface finishes. These surfaces may be obtained by using micron and sub-micron size diamond slurries. Monocrystalline diamond particles have a reduced number of sharp cutting points and edges, exhibit irregular shape and are thus more aggressive and prone to random scratching. As opposed to regular monocrystalline diamond particles, the micron size surface etched monocrystalline diamond particles exhibit an increased number of less sharp cutting points and edges. When embedded in the lapping plate and/or incorporated in the slurry which is dripped onto the lapping plate, the surface etched monocrystalline diamond particles are capable of delivering higher surface finishes and less random scratching compared to regular unetched monocrystalline diamond particles.
High pressure-high temperature (HP-HT) sintering of diamond particles into a coherent polycrystalline diamond body/compact (PCD) is achieved either by infiltration of metal, such as cobalt from tungsten carbide-cobalt substrate, or by mixing the diamond particles with a metal powder, such as cobalt, or combinations of metal powders, such as cobalt and tungsten carbide.
Cleanliness of the surface of diamond particles is another characteristic of a strong diamond bonding regardless of whether mechanical or chemical bonding mechanisms are involved. When incorporated in slurries or compounds, surface cleanliness of diamond particles allows for good particle dispersion. Moreover, cleanliness of the surface of diamond particles is important for the high pressure-high temperature sintering of diamond particles into an abrasive body/compact, which requires forming of diamond to diamond “bridges” via covalent bonding of sp3 hybridized carbon atoms.
At elevated temperature, diamond is not chemically inert and it can be eroded by oxygen and oxygen compounds, molten metals and hydrogen. Thermo-chemical etching of diamond can be achieved by using molecular oxygen, potassium nitrate (KNO3), or water vapor.
There are a number of known processes used to etch the surface of diamond particles. For example, one method of etching diamond particles involves heating the diamond particles in oxygen or KNO3 as discussed in “Etching of Diamond in Properties, Growth and Applications of Diamond” M H Nazare and A J Neves, Eds. INSPEC, pp 115. U.S. Pat. No. 5,344,526 discusses the heating of diamond particles in an oxygen atmosphere. U.S. Pat. No. 6,565,618 heats diamond particles in a non-oxidizing atmosphere or vacuum. Other methods involve heating the diamond particles embedded in metal powder while exposed to hydrogen or hydrogen-containing gas, (U.S. Pat. No. 5,035,771) and heating the diamond in air in the presence of metal or metal oxides (US Patent Application Publication No. 2010/0213175 A1).
However, these techniques do not provide sufficient etching concurrently with minimal loss of diamond material, do not provide a good control over the etching process, and lead to contamination of the diamond surface. Furthermore, heating of diamond particles in potassium nitrate, or embedded in metal powders while exposed to hydrogen or hydrogen-containing gas, are chemical reactions that are difficult to control, and require additional processing steps to remove the resulting chemicals/chemical compounds and clean the recovered diamond particles.